08 HJOUT'S IIYDllOGRAPHIC-BIOLOGICAL STUDIES 



place (110-120 metres). On February 15th, when spawning had taken 

 place, a temperature of 5° was first found at a depth of 120 metres; 

 and on March 1st the temperature at the surface was OS" ; at 40 

 fathoms, I'b" ; at 80 fathoms, 3"9° ; and even at 120 fathoms, only 

 4'3°, indicating conditions similar to those which prevailed in 1881. 



It thus appears to be satisfactorily determined that the influx of 

 herrings along shore during the spawning season depends on the 

 temperature of the water, which is an index of the prevailing salinity 

 and currents. 



The fish come right up to land during warm — often stormy — 

 winters; but in cold winters, when the Baltic current flows along the 

 coast, and when a thick layer of cold water covers the shallow spawning 

 places, the shoals of herring stop far out on the outer margins of the 

 shallows. 



The explanation which Hjort adduces is of the following character. 

 Sars showed that during the greater part of the year the herring and 

 cod keep out to the open sea, the herring far out in the surface layers, 

 the cod on the edge* of the coastal banks, and thence possibly far out 

 in the Northern Ocean at a similar depth. 



In both places the water in winter is salt " Atlantic water," and the 

 temperature is probably from 6° to 7° C. (Jide Mohn's charts.) 



Accordingly, when the large shoals approach the shores to spawn, 

 they may enter salt water of approximately the same temperature 

 (North Sea water at 5° or more), when they will continue their course 

 without interruption up to the shallow beaches ; or they may encounter 

 a deep layer of cold, comparatively fresh water (Baltic and bank 

 water, under 5°) all along the coast. 



In the latter case the conditions are so different from those prevailing 

 at the places from which the fish have migrated that the fish make 

 a halt : " The fish mope " — they say in the Lofotens of the cod ; " The 

 herring want stirring up " — the}^ say on the west coast. 



In each region, under the conditions which have been described, the 

 fishery is a failure. 



As to the relative importance to the fish of the two factors 

 " temperature " and " salinity " Hjort is silent. For the Norwegian 

 fisheries a knowledge of this point may be superfluous, since the two 

 factors work together; but for English fisheries further discrimination 

 may be of considerable importance, since we have no single agency 

 of the magnitude of the Baltic current that is capable of inducing 

 such extensive changes — temperature and salinity alike — in the quality 

 of the water around our coasts. 



2. The Fast Coast Autumn Herring Fishery. — The autumn herring 

 fishery on the East Coast of Norway is due, according to Hjort, to the 



